Torque from Force
Turning effect of a force applied at radius r.
Formula
Live Calculator
MembersVariables
Example
200 N on a 0.3 m wrench: τ = 60 N·m
How it works
This formula calculates how strongly a force tends to rotate an object about a pivot, such as a nut on a wheel or a bolt on an engine part. It works because the same force creates more turning effect when it is applied farther from the pivot, so a longer lever arm gives more torque. In this basic form, the force is assumed to act at right angles to the lever arm; if it acts at an angle, only the perpendicular part contributes.
When to use it
Use this when you want to find the turning effect produced by a push or pull on a spanner, wrench, pedal, lever, or crank. It is common in automotive and engine problems involving tightening bolts, turning shafts, and understanding mechanical advantage.
Worked example, step by step
A mechanic applies a force of 150 N to the end of a 0.40 m wrench. Use τ = F × r Substitute the values: τ = 150 × 0.40 Calculate: τ = 60 N·m Final answer: the torque is 60 N·m
Common mistakes to avoid
- Using the full length of the tool instead of the distance from the pivot to where the force is applied
- Forgetting to use metres for the lever arm, which gives the wrong units
- Assuming any force creates torque equally, even when the force is not applied perpendicular to the lever arm
Did You Know?
A longer breaker bar multiplies your torque — the reason stubborn wheel nuts finally give way.
Share this formula
More in Automotive & Engines
View allPower from Torque & RPM
IntermediateEngine power in kW from torque and rotational speed.
Horsepower from Torque (Imperial)
BasicHorsepower from torque (lb-ft) and engine rpm.
Compression Ratio
IntermediateRatio of cylinder volume at bottom vs top of the stroke.
Engine Displacement
BasicTotal swept volume of all cylinders.
Gear Ratio
BasicRatio of driven to driving gear teeth.
Vehicle Speed from RPM
IntermediateRoad speed from engine rpm, gearing and tyre diameter.